One overall improvement that could be made (perhaps to the FF error console in general) would be allowing you to sort by timestamp. By default new error messages come at the bottom. Displaying new ones at the top might be more useful for this extension, given limited screen real-estate.
I like this idea, but I think the icon in the status bar could be utilized better perhaps by providing notification when a new error is logged to the console. Also, it would be nice if height was saved across multiple sessions instead of reverting to the default of 300pixels. A good web development workflow simplifier, though.